The present invention relates to an electronic apparatus and clock generating method thereof, and more particularly, to an electronic apparatus capable of using a single reference oscillator to generate baseband clocks corresponding to different communications standards and clock generating method thereof.
Generally, in a wireless communications system, a communications module receives data signals from a base station (BS), and obtains corresponding data by means of frequency down-converting, demodulation, decoding, etc. However, when a frequency offset between the communications module and the corresponding BS is too large, accuracy of the demodulation operation may be corrupted. For ensuring demodulation quality of the communications module, it is essential to eliminate the frequency offset (i.e. carrier frequency offset) between the communications module and the corresponding BS.
Please refer to FIG. 1, which is a schematic diagram illustrating frequency adjustment of a prior art communications module during a signal receiving procedure. In the signal receiving procedure, a mixer of the communications module multiplies a carrier clock with the received data signals. The carrier clock may be generated and outputted from a baseband processing unit with reference to a baseband clock. A frequency of the carrier clock provided for the mixer should be identical to a frequency of a BS carrier clock for accurate demodulation, and a communications block operates to remove a carrier frequency offset between the communications module and the BS when the carrier frequency offset is detected. In FIG. 1, a baseband processing unit adjusts a frequency of a baseband clock by using an Automatic Frequency Control (AFC) unit when a frequency offset is obtained at T1. Supposing a frequency offset between the communications module and the corresponding BS is estimated as Δf as shown in FIG. 1, the frequency offset Δf may be removed by using the AFC unit to adjust a frequency of the baseband clock by a frequency variation β. By adjusting the frequency of the baseband clock outputted from the frequency synthesizer by the frequency variation β, the frequency of the carrier clock becomes the same as that of the BS carrier clock.
With the development of electronic technologies, a modern electronic apparatus, such as a mobile device, may support more than one communications service, such as GSM/GPRS/EGPRS (GGE), Bluetooth, Wireless Fidelity (WiFi), Worldwide Interoperability for Microwave Access (WiMAX) wireless communications service, power line communications (PLC), and so on. A modern mobile electronic device may contain many communications blocks to provide communications services corresponding to different communications standards, respectively. In addition, for reducing the design cost, a designer may be asked to integrate system-on-chips (SOCs) designed for providing communications services corresponding to different communications standards. Due to strict specifications of different communications standards, each SOC may need a precise oscillator (e.g. a crystal oscillator) to generate baseband clocks for different communications modules. However, the cost of the precise oscillator is very high. For reducing the production cost, all the SOC may share a single precise oscillator. In such a situation, how to share a single precise oscillator for different SOCs has become a goal in the art.